1. Field of the Invention
The present application relates generally to downhole tools for use in well bores, as well as methods of using such downhole tools. In particular, the present application relates to downhole tools and methods for plugging a well bore.
2. Description of Related Art
Prior downhole tools are known, such as hydraulic fracturing plugs and bridge plugs. Such downhole tools are commonly used for sealing a well bore. These types of downhole tools typically can be lowered into a well bore in an unset position until the downhole tool reaches a desired setting depth. Upon reaching the desired setting depth, the downhole tool is radially expanded into a set configuration. Once the downhole tool is set, the downhole tool acts as a plug to seal the tubing or other pipe in the casing of the well bore.
While lowering, a downhole tool may encounter internal diameter variations within the well bore. Downhole tools are typically sized according to the internal diameter of the well bore. If variations within the well bore are severe enough, the downhole tool will either be prevented from lowering to the correct depth or may fail to fully seal. Additionally, when setting the downhole tool, excessive pressure can result on selected components of the downhole tool resulting in shear forces that exceed tool tolerances. In such applications, components within the downhole tool can shear or break away from the tool resulting in a possible failure to set and fully seal the well bore.
When it is desired to remove many of these types of tools from a well bore, it is frequently simpler and less expensive to mill or drill them out rather than to utilize multiple complex retrieving operations. In milling, a milling cutter is used to grind the plug out of the well bore. Milling can be a relatively slow process. In drilling, a drill bit is used to cut and grind up the components of the downhole tool to remove it from the well bore. Drilling is typically a much faster process as compared to milling.
Drilling out a plug typically requires selected techniques. Ideally, the operator employs variations in rotary speed and bit weight to help break up the metal parts and reestablish bit penetrations should bit penetrations cease while drilling. A phenomenon known as “bit tracking” can occur, wherein the drill bit stays on one path and no longer cuts into the downhole tool. When this happens, it is often necessary to pick up the bit above the drilling surface and rapidly re-contact the bit with the packer or plug and apply weight while continuing rotation. This aids in breaking up the established bit pattern and helps to reestablish bit penetration. However, operators may not recognize when bit tracking is occurring. Furthermore, when operators attempt to rapidly re-contact the drill bit with the downhole tool, the downhole tool may travel with the drill bit as a result of unequalized pressure within the well bore. This is seen typically as drilling has passed through the slip means, thereby decreasing the downhole tool's grip within the well bore. The result is that drilling times are greatly increased because the bit merely wears against the surface of the downhole tool rather than cutting into it to break it up. Both milling and drilling result in the downhole tool being destroyed and/or lost with no capability to reuse any portion of the downhole tool.
Although great strides have been made in downhole tools, considerable shortcomings remain.
While the system and method of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the application to the particular embodiment disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the process of the present application as defined by the appended claims.